The present invention relates to a press machine for pressing while moving a slide up and down by rotating a crankshaft.
A press machine is formed to be able to operate to press by driving a drive mechanism (for example, crank mechanism or the like) by a drive source (for example, electric motor) while moving up and down a slide connected thereto.
Press speed is defined as a time period required for moving a slide up and down between a top dead center and a bottom dead center once and is designated as revolution speed of a drive source (electric motor). Specifically, the press speed is designated as SPM (Stroke Per Minute). That is, when importance is given to productivity, speed of a drive source (electric motor) is controlled by using a speed control system (speed control apparatus). Target speed is adjusted in correspondence with whether a gear or a speed reducer is interposed between the electric motor and the crankshaft.
Meanwhile, in pressing, a product shape is determined by determining a position of a slide and therefore, when importance is given to a product accuracy, a drive source (electric motor) is subjected to position control by using a position control system (position control apparatus). For example, position control is carried out while inputting to switch a target position at every constant cycle in accordance with slide motion constituting a corresponding relationship between a crankshaft angle and a slide position.
Further, also in the case of the position control system, at a final stage thereof, similar to the case of the speed control system, the drive source (electric motor) is subjected to speed control. Further, also in the case of the speed control system, at a first stage, similar to the case of the position control system, there is frequently a case of setting the speed as a relationship (position) between time and rotational angle of the crankshaft.
However, depending on a kind of a product and a method of working the product, for example, when a helical gear or the like is forged (pressed), there is also a case in which pressing force effects stronger influence on the acceptability of the product than position. In this way, according to the prior art, a pressure control system (hydraulic press machine) constituting the drive source by hydraulic pressure is used and for example, there is carried out a pressure control for maintaining slide pressing force at a predetermined pressing force while inputting to switch target pressing force at every constant cycle in accordance with a corresponding relationship among a position of a slide connected to a hydraulic cylinder, a crankshaft angle and pressing force.
Meanwhile, according to a press (hydraulic press machine) constituting the drive source by hydraulic pressure, in view of the structure, energy loss by heat generation and cooling is considerable and there also poses a problem in view of environment such as oil leakage. It is indicated from such a point of view that adoption of a hydraulic press machine is intended to be avoided.
Hence, it has been tried to use a pressure control section constituting a drive source by a linear motor enabling a motion similar to that of the case of a hydraulic press machine and having a characteristic in which pressing force is prosectional to motor current without using a crank mechanism (linear motor type press machine). However, in the case of the linear motor type, in view of the structure, it is difficult to achieve large thrust. Further, since a coil side unit and a permanent magnet side unit having strong attractive force are constituted by separate units, it is difficult to deal therewith when the permanent magnet side unit is integrated to the press machine.
In the case of a rotating electric motor type having a crank mechanism, the problem of the linear motor type is not posed and torque can be increased by interposing a speed reducer or the like. However, in the case of the rotating electric motor type, a crank mechanism constituting a rotation-linear line converting mechanism is indispensable and therefore, regardless of presence or absence of a speed reducer or a gear, there poses a problem that a relationship between slide pressing force and motor torque is changed and the pressing force becomes infinite theoretically at a bottom dead center (or, immediately before bottom dead center). Further, in the case of a ball screw shaft type adopting a ball screw shaft mechanism in place of a crank mechanism, similar to the case of the linear motor type, it is difficult to achieve large thrust. Further, in forming a product, pressing force is exerted to a ball screw, friction force is increased and wear of the ball screw poses a problem.
In this way, in the prior art, when, for example, a helical gear or the like is forged (pressed), although it is recognized that there is unresolved constitutional problems (large energy loss) or environmental problems, the hydraulic press machine is obliged to be adopted by acquiescing to the problems as a risk.
Further, the press machine of the conventional art for pressing while moving the slide up and down by rotating the crankshaft, is constituted to selectively transmit and separate rotational energy accumulated in a flywheel to and from the crankshaft via clutch & brake.
In such a press machine, die height setting operation is carried out by adjusting a position of an upper die in an up-and-down direction or a position of a lower die in the up-and-down direction before a press operation. A position of a bottom dead center of a slide in this case is determined by a crank mechanism (crankshaft). Therefore, even when respective constituent elements (for example, connecting rod, frame) are elongated or contracted by heat generation or the like during the press operation, a position of a bottom dead center (and therefore, die height) necessary for canceling the elongation or the contraction cannot be adjusted.
That is, adjustment of the bottom dead center position (die height) is carried out by, for example, manually or electrically driving to adjust a vertical position adjusting apparatus mounted to a side of a bolster (lower die) or a slide position adjusting apparatus mounted to a side of the slide (upper die) after stopping the press operation.
Meanwhile, among requests accompanied by further diversification and high quality formation, that is, among requests to carry out plastic deformation (pressing) by a press machine, there are a case of intending to carry out forming by giving importance to the position of the bottom dead center of the slide and a case of intending to carry out forming by giving importance to pressing force of the slide.
In this case, when the bottom dead center position of the slide is delicately changed during the press operation, even with the same mold (upper and lower dies) and a work (material) having the same shape or the like, the pressing force of the slide is changed. Further, the pressing force of the slide is complicatedly changed also by an accuracy (error or dispersion) of a thickness of the work (material) which has nothing to do with the change in the bottom dead center position of the slide.
Hence, in order to meet the request of intending to carry out forming by giving importance to the pressing force of the slide, the pressing force of the slide has been tried to adjust during a press operation by using a press machine which is not provided with a crank mechanism (crankshaft) (for example, a trial machine (ball screw type press machine) constructed to be able to move the slide in the up-and-down direction by rotating the ball screw by an electric motor).
According to a trial result by the ball screw type press machine, adjustment of the pressing force per se is possible. However, the pressing force is directly exerted to the ball screw as reaction and therefore, wear of the ball screw is enormous. Therefore, the ball screw type press machine is not suitable for a press machine needing large pressing force. Similarly, also the case of directly driving the slide by constituting the drive source by the linear motor (linear motor type press machine) is not suitable for large pressing force.